ERROR plpy.execute result do not support attribute status

[BaiShaoqi]

Expected behavior

 INFO:  True
 CONTEXT:  PL/Python function "result_metadata_test"
  result_metadata_test
 ----------------------
                     2
 (1 row)

Actual behavior

 INFO:  True
 ERROR:  PL/Container client exception occurred:
 DETAIL:
  Exception occurred in Python during function execution
  Traceback (most recent call last):
   File "<string>", line 6, in result_metadata_test
 AttributeError: 'list' object has no attribute 'status'

Step to reproduce the behavior

create function result_metadata_test(cmd text) returns int as $$
# container: plc_python_shared
plan = plpy.prepare(cmd)
plpy.info(plan.status())
result = plpy.execute(plan)
if result.status() > 0:
    return result.nrows()
else:
    return None
$$ language plcontainer;

SELECT result_metadata_test($$SELECT 1 AS foo, '11'::text AS bar UNION SELECT 2, '22'$$);